Infant mice and ligated ileal loops of adult rabbits will be used as models for the evaluation of flagellar vacccnes prepared from V. cholerae and enterotoxigenic E. coli. Depolymerized and repolymerized flagellin from V. cholerae, which give a single band in polyacrylamide gel electrophoresis, afford excellent protection in rabbits as judged by the number of challenge organisms required to yield maximum fluid accumulation. The flagellin plus toxoid is an even better vaccine. Similar tests will be carried out using E. coli as the source of the flagella and the labile toxin. Fluid accumulation in ligated ileal loops of rabbits will be used to measure immunity. Cross-protection between the two species of bacteria, which is afforded by toxin or toxoid alone, will be tested when flagella are part of the vaccine. Flagellar vaccines from Salmonella typhimurium will be prepared and used to immunize adult mice. These animals will be challenged orally to see whether anti-motility antibody protects against the invasiveness of the bacteria and thereby reduces susceptibility to this highly mouse-virulent pathogen.